Sneak analysis

A sneak circuit or path is an unintended energy route, which can allow an undesired function to occur, prevent desired functions from occurring, or adversely affect the timing of functions. Sneak circuit analysis or sneak analysis is performed to identify ways in which built-in design characteristics can either allow an undesired function to occur or prevent desired functions from occurring. Even though most sneak circuits and most sneak circuit analysis... 

The sneak circuit analysis (SCA) (also known as sneak analysis) is a system safety analytical technique used to identify and evaluate the different possible ways in... 

Buratto, D. L. and Goody, S. G. June 1982. Sneak Analysis Application Guidelines. 

Clardy, R. C. 1977. Sneak analysis An integrated approach. International System Safety Conference Proceedings, 1977. New York System Safety Society. 

Sneak analysis is a technique for identifying latent hazards which arise from design or systematic errors but not from component caused failures (Whetton and Armstrong, 1994, lECffSO 31010, 2009). 

Whetton, C. Armstrong, W. 1994. Sneak analysis of batch processes. Journal of Hazardous Materials, 38, 257-275. 

Whetton, C.P. 1992 Thermohydraulic sneaks. In Proc. Sneak Analysis Workshop. ESA-WPP033, European Space Agency, ESTEC, Noordwijk, The Netherlands. 

In hardware, sneak analysis provides a powerful alternative to functional analysis. In the variant which h b used, sneak oath analysis, the tracing procedure starts by identifying "targets", that is items of hardware which can cause an accident if activated at the wrong time, or items of hardware which must operate in order to ensure safefy. 

Bougnol C., Dore B., Taylor J.R. Development of Sneak Analysis procedures and Computer tools. ESREL conference, Munich 1993, Elsevier pub. 

HAZOP/FAULTTREE ANALYSIS PROCESS/ SNEAK ANALYSIS... 

Sneak analysis Looks for unintended paths (flows) within an electrical system. 

Although risk analysis of new facilities is required by Ref. 39, the method of conducting the analysis is left quite open. The reference suggests fault hazard analysis, fault tree analysis, or sneak circuit analysis. Ref. 41 is an example of a thorough hazards evaluation and risk analysis for a new facility at Radford Army... 

The recommended techniques for preliminary hazard analysis are energy trace and barrier analysis (ETBA) and failure modes and effects analysis (FMEA). Recommended techniques for system and subsystem hazard analyses are FMEA, fault tree analysis (FTA), common cause analysis, sneak circuit analysis (for electrical, electronic, and some hydraulic or pneumatic circuits) and, of course, software hazard analysis for software. 

Based on the results of the PHA, recommendations made by 30% review boards, and guidance provided in the system safety program plan, detailed hazard analyses are made of specified (critical) subsystems. The techniques for these SSHAs are as outlined in the system safety program plan or as selected by the SSWG. Failure modes and effects analysis (FMEA) and/or fault tree analysis (FTA) are generally the techniques of choice. Software hazard analysis, common cause analysis, and/or sneak circuit analysis may also be appropriate. 

An important feature of sneak circuit analysis is that the sneak paths being investigated are not the result of a component failure. They are rather the result of the circuit design. The sneak paths may show up only on rare occasions when the switches (or valves) in the circuit are in a unique configuration. 

Sneak circuit analysis is usually inductive and can be very difficult to perform without the software to aid in producing network trees and other graphics. Much of this software is proprietary, and a large portion of the sneak circuit analysis work done to date has been accomplished by large aerospace and weapons contractors (notably Boeing and General Dynamics). 

The most common approach to sneak circuit analysis involves visual clues found by comparing circuits with the five basic topographs shown in Figure 20-1. Nearly every circuit can be broken down into combinations of these topographs. 

Successful sneak circuit analysis requires a skilled analyst and great care. Unfortunately, sneak circuit analysis is frequently performed with... 

Most sneak circuit analysis has been done by one or two large defense and aerospace contractors. Why ... 

To illustrate this point, this chapter addresses two system safety analytical methods that have been developed as a result technological improvements the sneak circuit analysis and the software hazard analysis. Each is briefly discussed here to demonstrate its applicability and utility in the practice of industrial safety and health. 

Basically, the ways in which sneaks can occur and the potential results of these events can be grouped into four primary categories, as indicated in Table 15.1. Each type, if possibly applicable to a specific system, requires separate analysis. 

Although software hazard analysis is a separate system safety teclmique and is discussed later in this chapter as such, a review of compiler and/or assembly languages as well as any applicable system reference manuals and interface control specifications is advisable during the SCA. Sneak risks have been discovered as a result of improper or inappropriate software command initiatives. 

Figure 15.1 Sample sneak circuit analysis worksheet.

The system safety analysis techniques known separately as sneak circuit analysis and software safety analysis have been developed in an effort to address these concerns over system safety and reliability assurance. Although various types of sneak hazards can be identified by analysis, and a variety of software hazard analysis techniques are commonly used, each method is concerned primarily with the same essential objective explained throughout this text hazard risk elimination or reduction to acceptable levels. 

CASCA Computer-aided sneak circuit analysis... 

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